Aqueous cleaning processes are a mainstay of both domestic and industrial textile fabric washing. On the assumption that the desired level of cleaning is achieved, the efficacy of such processes is usually characterised by their levels of consumption of energy, water and detergent. In general, the lower the requirements with regard to these three components, the more efficient the washing process is deemed. The downstream effect of reduced water and detergent consumption is also significant, as this minimises the need for disposal of aqueous effluent, which is both extremely costly and detrimental to the environment.
Such washing processes, whether involving domestic washing machines or their industrial equivalents (usually referred to as washer extractors) involve aqueous submersion of fabrics followed by soil removal, aqueous soil suspension, and water rinsing. In general, the higher the level of energy (or temperature), water and detergent which is used, the better the cleaning. The key issue, however, concerns water consumption, as this sets the energy requirements (in order to heat the wash water), and the detergent dosage (to achieve the desired detergent concentration). In addition, the water usage level defines the mechanical action of the process on the fabric, which is another important performance parameter; this is the agitation of the cloth surface during washing, which plays a key role in releasing embedded soil. In aqueous processes, such mechanical action is provided by the water usage level in combination with the drum design for any particular washing machine. In general terms, it is found that the higher the water level in the drum, the better the mechanical action. Hence, there is a dichotomy created by the desire to improve overall process efficiency (i.e. the reduction of energy, water and detergent consumption), and the need for efficient mechanical action in the wash. For domestic washing in particular there are defined wash performance standards specifically designed to discourage the use of such higher levels in practice, in addition to the obvious cost penalties which are associated with such usage.
Current efficient domestic washing machines have made significant strides towards minimising their consumptions of energy, water and detergent. EU Directive 92/75/CEE sets a standard which defines washing machine energy consumption in kWh/cycle (cotton setting at 60° C.), such that an efficient domestic washing machine will typically consume <0.19 kWh/kg of washload in order to obtain an ‘A’ rating. If water consumption is also considered, then ‘A’ rated machines use <9.7 liters/kg of washload.
The most recent system in the EU (arising from Commission Delegated Regulation 1061/2010, introduced from 20 Dec. 2011) has, however, seen a switch to a new rating system for domestic washing machines. This considers annualised energy and water consumptions, and derives an energy efficiency index (EEI) based on a defined weekly set of wash cycles (3 off 60° C. at full load, 2 off 60° C. at half load, and 2 off 40° C. at half load). The total energy consumption of these washes (plus weighted values for the ‘off mode’ and ‘left-on’ mode power consumptions) is then averaged to a daily figure (by division by 7). The resulting figure is then multiplied by 220—the assumed average number of washes per annum, to calculate the annual energy consumption (AEc) in KWh. The EEI is then calculated by dividing the AEc by a standard annual energy consumption (SAEc=[47×c]+51.7), where c is the washload capacity for the machine. An EEI value of <46 results in an A+++ energy efficiency rating. A similar approach is taken with the water consumption to arrive at the AWc (the water consumption for the same weekly set of wash cycles, averaged to daily consumption and annualised). This value is, however, simply displayed as an annual consumption in liters/annum.
Detergent dosage is then driven by manufacturer recommendations but, again, in the domestic market, for a concentrated liquid formulation, a figure of 35 ml (or 37 g) for a 4-6 kg washload in soft and medium hardness water, increasing to 52 ml (or 55 g) for a 6-8 kg washload (or in hard water or for very dirty items) is typical (see, for example, Unilever pack dosage instructions for Persil® Small & Mighty). Hence, for a 4-6 kg washload in soft/medium water hardness, this equates to a detergent dosage of 7.4-9.2 g/kg whilst, for a 6-8 kg washload (or in hard water or for very dirty items), the range is 6.9-9.2 g/kg.
Energy, water and detergent consumptions in the industrial washing process (washer extractors) are considerably different, however, and usages all three resources are less constrained, since these are principal factors in reducing cycle time—which is, of course, more of a consideration than in the case of domestic processes. For a typical industrial washer extractor (25 kg washload rated and above), energy consumption is >0.30 kWh/kg, water usage is at ˜20 liters/kg, and detergent is much more heavily dosed than for domestic washing. The exact level of detergent used will depend on the amount of soiling, but a range of 18-70 g/kg is representative.
Thus, it can be taken from the above discussion that it is the performance levels in the domestic sector which set the highest standard for an efficient fabric washing process, and that these are: an energy consumption of <0.19 kWh/kg or an EEI of <46, a water usage of <9.7 liters/kg, and a detergent dosage of approximately 8.0 g/kg (8.5 ml/kg). However, as previously observed, it is becoming increasingly difficult to reduce the water (and, hence, energy and detergent) levels in a purely aqueous process, due to the minimum requirement to wet the fabric thoroughly, the need to provide sufficient excess water to suspend the soil removed in an aqueous liquor and, finally, the need to rinse the fabric.
Heating of the wash water is then the principal use of energy, and a minimum level of detergent becomes necessary in order for an effective concentration to be reached at the operating wash temperature. Means to improve mechanical action without increasing the water level used would, therefore, make any aqueous wash process significantly more efficient (i.e. yield further reductions in energy, water and detergent consumption). It should be noted that mechanical action itself has a direct effect on the detergent level, since the greater the level of soil removal which is achieved through physical force, the less that is required of the detergent chemistry. However, increasing the mechanical action in a purely aqueous washing process has certain associated drawbacks. Fabric creasing readily occurs in such processes, and this acts to concentrate the stresses from mechanical action at each crease, resulting in localised fabric damage. Prevention of such fabric damage (i.e. fabric care) is of primary concern to the domestic consumer and the industrial user.
In the light of these challenges which are associated with aqueous washing processes, the present inventors have previously devised a new approach to the problem, which allows the deficiencies demonstrated by the methods of the prior art to be overcome. The method which is provided eliminates the requirement for the use of large volumes of water, but is still capable of providing an efficient means of cleaning and stain removal, whilst also yielding economic and environmental benefits.
Thus, in WO-A-2007/128962 there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. Preferably, the substrate is wetted so as to achieve a substrate to water ratio of between 1:0.1 to 1:5 w/w, and optionally, the formulation additionally comprises at least one cleaning material, which typically comprises a surfactant, which most preferably has detergent properties. In preferred embodiments, the substrate comprises a textile fibre and the polymeric particles may, for example, comprise particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers, but are most preferably in the form of nylon beads.
The use of this particle-based cleaning method, however, presents a requirement for the cleaning particles to be efficiently separated from the cleaned substrate at the conclusion of the cleaning operation, and this issue is addressed in WO-A-2010/094959, which provides a novel design of cleaning apparatus requiring the use of two internal drums capable of independent rotation, and which finds application in both industrial and domestic cleaning processes.
In co-pending WO-A-2011/064581, there is provided a further apparatus which facilitates efficient separation of cleaning particles from the cleaned substrate at the conclusion of the cleaning operation, and which comprises a perforated drum and a removable outer drum skin which is adapted to prevent the ingress or egress of fluids and solid particulate matter from the interior of the drum, the cleaning method requiring attachment of the outer skin to the drum during a wash cycle, after which the skin is removed prior to operating a separation cycle to remove the cleaning particles, following which the cleaned substrate is removed from the drum.
In a further development of the apparatus of WO-A-2011/064581, there is disclosed in co-pending WO-A-2011/098815 a process and apparatus which provides for continuous circulation of the cleaning particles during the cleaning process, and thereby dispenses with the requirement for the provision of an outer skin.
The apparatus and methods disclosed in the foregoing prior art documents have been highly successful in providing an efficient means of cleaning and stain removal which also yields significant economic and environmental benefits.
In co-pending PCT Patent Application No. PCT/GB2011/052117 the polymeric particle-based cleaning method, and the separation of said cleaning particles from the cleaned substrate, are both further improved by careful control of polymeric particle size, shape and density, as well as process parameters. A cleaning process is achieved which facilitates excellent cleaning performance at surprisingly low cleaning temperatures (i.e. low energy), and with reduced levels of added detergents, whilst also maintaining the original low water consumption. In the present invention, even further improvements to this cleaning process are achieved by the use of enhanced methods which move away from the use of only polymeric cleaning particles.
The present inventors have now established that certain non-polymeric particles can enhance the mechanical action in the wash process such that, most particularly in combination with polymeric particles, there is a surprising benefit achieved in overall cleaning performance. Specifically, high density (>3.5 g/cm3) non-polymeric particles of similar size and shape to those described in PCT Patent Application No. PCT/GB2011/052117 have been found to provide this enhanced effect. The non-polymeric particles are significantly more dense than the polymeric particles they are mixed with, due to the nature of the different materials used (the specific examples of non-polymeric particles are glass and metal). Hence, the benefit of the present invention is in still further enhancing cleaning performance even at the already low cleaning temperatures, reduced levels of added detergents, and low water consumptions disclosed in PCT Patent Application No. PCT/GB2011/052117.
As previously discussed, effective targets for these savings would be significant reductions below an energy consumption of 0.19 kWh/kg or an EEI of <46, a water usage of <9.7 liters/kg, and a detergent dosage of approximately 8.0 g/kg (8.5 ml/kg). The current invention allows a new washing process capable of achieving these targets, whilst also facilitating reduced localised fabric damage in the washed substrate by virtue of the increased uniformity of the mechanical action of the particles with the fabric surface.
In addition, removal levels of the non-polymeric particles from the fabric washload at the end of the cleaning process are at least as efficient as for the removal of polymeric particles in PCT Patent Application No. PCT/GB2011/052117.